Controlling
Unstable Systems

Paul Castle

Tubes
of water are a key component in the hydraulically balanced beam
system designed and built by mechatronics students.

When a system is inherently unstable, it takes a creative control system
to maintain balance. A group of Rensselaer seniors and first-year graduate
students demonstrated this spring that they are mechanical engineers with
sufficient understanding of computer controls to create such systems.
Students in the second course of a two-course sequence in mechatronics
presented four projects they had designed, analyzed, modeled, and built
during spring semester: a hydraulically balanced beam system, a ball-on-beam
balancing system, a ball-on-plate balancing system, and a device that
encompassed two inverted pendulum systems, rotary and arm-driven.
Mechatronics integrates mechanical engineering, control engineering,
electronics, and computer science into the design process, according to
Kevin Craig, associate professor of mechanical engineering and originator
of the course. Mechatronics engineers are needed because electronics and
computer controls have became so common that mechanical engineers must
consider them from the earliest stage of design.
In the hydraulically balanced beam system, for example, a horizontal
bar rotated about a pivot point, much like a seesaw. Two cylinders of
water were installed atop the bar and a pumping system could move water
back and forth between them. The students demonstrated that when they
gave the device a shove and started it rocking up and down, the computer
control system operating the pumps shifted sufficient water from one cylinder
to another to bring the bar back into horizontal balance.
Visitors from industry and from local schools viewed the presentations,
which were held in the School of Engineering's newest studio classroom,
a large amphitheater in which those seated around the room could get a
close-up look on flat-panel displays located on their desks.